This invention relates to a dielectric material useful in plasma display panels (PDPs) and, in particular, to a dielectric composition used for forming a light transparent dielectric layer on a front glass plate of a high strain point in PDPs.
A plasma display panel is known as a self-luminescent type flat display having excellent properties of such as a small weight, a thin type etc. and draws considerable attention because of its possibility of a large screen face.
Generally speaking, a PDP has a front glass plate on which a plurality of electrodes are disposed for generating plasma discharge by cooperation with electrodes deposited on a rear glass plate confronting the front glass plate with a gap therebetween. A light transparent dielectric layer is formed with a thickness of about 30–40 micrometers on the glass plate to cover the electrodes so as to maintain the plasma discharge generated.
Usually, the front glass plate is made of soda-lime glass or other high strain point glass and Ag is used for the electrodes, while the light transparent dielectric layer is formed from dielectric material comprising low fusion point glass powder, for example, high Pb-content glass powder.
When forming the light transparent dielectric layer, the dielectric material is fired or baked at the softening point of the low-fusion point glass powder so as to avoid the reaction with metal of the electrodes.
However, the conventional dielectric material has a problem that the glass powder and the Ag electrodes react with each other to make the dielectric layer color (change to yellow).
Further, it is important as known in the art that the dielectric material has various properties such as (1) thermal expansion coefficient compatible with glass plate, (2) firing temperature at 500–600° C., (3) excellent defoamability in firing to produce the dielectric layer of high light transmittance and high withstand voltage with a reduced amount of bubbles.
JP-A 11-21148 discloses a dielectric material using a glass powder of PbO—B2O3—SiO2—BaO glass which has the thermal expansion coefficient compatible with that of the high strain point glass plate. The PbO—B2O3—SiO2—BaO glass is rapid in viscosity change across the softening point and is, therefore, readily defoamed.
Although the dielectric material using PbO—B2O3—SiO2—BaO glass powder can provide a dielectric layer having a high light transmittance because of its excellent defoamability, it has a problem that the produced dielectric layer has residual large bubbles having diameters of 30 μm (micrometers) or more.